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Alois Zollner

LWF

Bavarian State Institute of Forestry
Section Biodiversity, Conservation and Hunting

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Author(s): Editorial office waldwissen.net – LWF
Editorial office: LWF, Germany
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Multifunctional mire protection in the forest

For more than 200 years, mires were systematically and intensively exploited by mankind. Today we know that mire protection is also good for climate protection. This has given new momentum to the renaturalisation of mires.

Content:

Graben im Rotter Forst
Fig. 1: Many mires show traces of earlier attempts to make them usable, such as this deep ditch that has its effect to this day (Picture: S. Müller-Kroehling).

In former times, mires were systematically drained to establish new production areas for agriculture and forestry. At the same time, peat was extracted as a valuable raw material, used mainly as a fuel and as litter material. In many regions, the use of peat meant that the high toll exerted on the forest by rights of use for fuel wood and litter was reduced. Today in Bavaria, peat extraction is largely a thing of the past.

Mire renaturalisation: tricky but multifunctional

Drainage measures and the subsequent use of the land have changed the natural condition of almost all mires permanently. Many mires have been carved up and divided by drainage ditches and peat extraction. Their peat beds are often subject to severe subsidence and decomposition, and characterised by considerable differences in relief. This is true for almost all larger raised bogs and transitional mires in Bavaria, and means that complete regeneration is often not possible.

Mire renaturalisation serves a whole set of other targets, including flood and climate protection as well as nature protection. Intact mires can act as buffers or at least mitigate the effects of extreme meteorological events in areas with high precipitation. If the hydrological features of mires can be restored to a near-natural condition, so that typical mire vegetation can grow there again, they bind CO2 permanently in the peat and thus act as carbon sinks. In mire renaturalisation at the moment, the focus tends to be on aspects of climate protection, but it is in fact always "multifunctional".

There is a long history of mire protection in Bavaria, so that measures to restore the natural hydrological characteristics of the mires have already been carried out on at least parts of almost all larger mire areas. Many of these measures have been successful, too, if not always on 100% of the area. In renaturalisation planning nowadays, digital models of the terrain are used to show the cross-sections of the bogs and their incline. This makes it easier to raise the water level successfully towards the ground surface (preferably 5-10 cm below surface layer), so that peat formation can begin again. A larger permanent area of water should not be created in the process. This would on the one hand result in the release of the gas methane, which has a strong effect on the climate, and it would also prevent colonisation by peat-forming vegetation. Only a few species typical of mires can become established in larger, open areas of water. Their preferred habitats are in fact the hollows and holes created for example when a mountain pine falls and its root plate is pulled out.

Mire and forest?

Moorrandwald
Fig. 2: Peatland edge forests occupy the edges of the wetland and protect the mire from harmful dehydration (Picture: B. Mittermeier).

When we think of mires, we often think of an open landscape of raised bogs, and our guiding principles for mire conservation are frequently derived from this picture of a largely treeless raised bog. We generally interpret conifer-dominated forest stands on peat bog sites, on the other hand, as being the final stage of a negative development. There are however at least three good reasons why we should include near-natural peatland forests more in our development of guiding principles for mire conservation:

  1. Originally, Bavaria’s mires - or at least significant parts of them - were often forested or sparsely stocked with slow-growing, stunted trees. Before human intervention, many mires had significant areas of sparse shrub vegetation, closely intertwined with the open areas.
  2. Where the peat bed has been changed irreversibly and subsidence and differences in relief are apparent in the bog, the water level can now no longer be raised sufficiently. In these areas, groves are now the potential natural vegetation.
  3. Intact and diverse peatland forests are just as suitable as a habitat for animals and plants specialising in mires (so-called tyrphobiont and tyrphophile species) as open mires. Many highly specialised species prefer complex areas including open, semi-open and relatively closed areas. Some of the species subject to strict protection prefer peatland forests in particular. The mountain pine (Pinus rotundata) - an endemic species in southern central Europe - features strongly in the stand structure of near-natural peatland forests. The Carpathian moor birches (Betula carpatica) are similarly important in the Rhön region.

The mainly spruce-dominated peatland edge forests of the Alps and Alpine foothill region and the mountains along the eastern Bavarian border are also valuable near-natural forests. Along with moor birch and Scots pine, spruce trees often make up the natural forest cover here.

Peatland edge forest for the mire climate

Übergang von Wald und Offenland
Fig. 3: There is no conflict of interest between mire and forest. Mosaics with diverse site characteristics and transitional areas from forest and open land are particularly rich in species typical of moors (Picture: E. Lohberger).

By binding CO2, mires do have an effect on the global climate, but they also have a very special local climate. Particularly in raised bogs, frosts may occur almost all year round, especially at night. In the summer months, temperatures of up to 70 °C are often reached at places without vegetation cover, and raised sites (hummocks) are temporarily subject to severe drying out.

For this special local climate, an intact peatland edge forest is also particularly important. It protects the mire not only from nutrient imports, but also from winds that may dry it out (oasis-effect). The peatland edge forest referred to as liverwort-spruce forest is naturally dominated by spruce, often mixed with moor birch, Scots pine, depending on the altitude and influence of mineral soil water in places silver fir, rowan (also known as mountain ash), black alder, crack willow and other mixed forest species. This peatland edge forest is an important habitat for diverse species and a natural spruce site.

The removal of intact peatland edge forests in order to promote rare species such as the moorland clouded yellow butterfly (Colias palaeno) or the black grouse (Tetrao tetrix) is completely unnecessary. These species can reach and colonise the centre of the mires through the forests or via the forest canopy. Such measures also significantly compromise the habitat for other typical moor species living there.

Species conservation in peat bogs

Hochmoorlaufkäfer
Fig. 4: The Carabus ground beetle (Carabus menetriesi pacholei Sokolar), priority species under FFH Directive 92/43, loves intact mires in particular, and also peatland forests (Picture: S. Müller-Kroehling).
 
Birkensplintkäfer-Ausbohrlöcher an Moorbirke
Fig. 5: Dead wood in peatland forests provides a habitat for many species (Picture: S. Müller-Kroehling).

On a large part of their area, mires are water-saturated. The natural hydrology is to be restored mainly by sealing off former drainage ditches. As soon as the water collects permanently again near the surface, plants typical of mires can grow again and carbon dioxide is sequestered, with a mitigating effect on climate change.

However, dried out mires in particular often offer refuge to species that need dryness and warmth in combination with low nutrient availability. Such habitats are no longer available because of the intensive use of land. In practice however, damming measures are only effective for partial areas because of the mentioned differences in relief. Sufficient "dry sites" or left-over ridges of peat usually thus remain in the renaturalisation area after re-wetting. Highly specialised, typical mire species that are adapted to the special habitat conditions of the peat bogs also benefit. Their conservation can only be guaranteed in mires - mires that preferably remain intact. In case of doubt, priority must be given to these species. Often the conservation of both valuable forest species and valuable moor and heathland species goes hand in hand. In general, there should not be any conflict between the conservation of species and restoration of the wetland.

In cases of doubt, the requirements of the specific species actually occurring in the mire should be analysed closely. The existing tree cover of near-natural peat-bog forests is quite possibly not only no problem, but may even be the preferred habitat of the species typical of the mire in this area.

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